The present invention relates generally to a formulation for the pretreatment of ferrous metals which are destined for plating operations, and more particularly to an improved composition for the preparation of aqueous pretreatment working solutions for ferrous metals.
Ferrous metals are frequently coated with protective and/or decorative metals. In order to prepare the surfaces of the ferrous metals for the plating or finishing operation, the surfaces must be treated so as to remove any residual oils which tend to attract and retain soil, and thereby rendering the metal surfaces receptive to plating. Residual soil, normally in the form of a soil retaining oil adversely affect the capability of the surface to receive a uniform and tightly adherent coating.
Examples of such metal coatings in wide usage today include zinc, chromium, and nickel, as well as others, each having its own specific function and purpose. Surface plating is performed on ferrous metals in order to provide protection from the environment, improved appearance, or improved electrical conductivity. Plating is ordinarily employed where the construction of the part if made totally of the metal plating, would be economically unjustified or economically unsound.
The final operation for the parts is normally the plating operation. Parts selected for plating normally require pretreatment for the purpose of cleaning the surface and rendering it receptive to the plating materials to be used. Frequently, electrodeposition is employed, although modified forms of deposition may be employed including electroless or the like. When the surfaces of the individual component parts are free of soils and foreign matter, they accept and adherently retain the metallic ions to be plated thereupon.
As examples of foreign materials which are frequently found on the surfaces of manufactured piece parts, the most common is soil retaining oil. Oils are normally used in the various manufacturing operations including stamping, grinding, polishing, buffing, handling and shipping. Each of these operations are responsible for providing surfaces of interfering soil. Examples of such oils are quenching oils, rustproofing oils, drawing oils, stamping and die lubricants, flushing oils, residues of various fats and waxes, as well as abrasives. These soils vary in their individual properties, and frequently are complex, leading to certain difficulties when attempts are made to provide a universal cleaner. The metal finishing of parts incorporating an electrodeposited finish has progressed significantly through the years, with continuing improvements bringing the process capability to the present form of preprogrammed automatic plating lines. Because of the multitude of products being employed, the large volumes of such products and the necessary economics, care must be taken to provide a surface which is both receptive and capable of adhering the metal finishing coat.
Among the operations employed in a plating line, either an automatic rack or a barrel plating system is employed. The configuration including the size and shape of the particular part will ordinarily determine the process to be utilized, and such preselection processes are well known. Parts which are large and complex are normally not effectively plated in a barrel system, but are alternatively fixtured to a rack. Alternatively, when the parts consist of smaller items including screws, nuts, electrical connectors and the like, they may be placed in bulk in a barrel which is rotated in the various stages of the plating cycle. The barrel is provided with holes or bores to enhance circulation of the plating solution, while being sufficiently small so as to prevent parts from inadvertant removal from the barrel.
After the parts have been disposed within the appropriate plating system, they are moved through the plating cycle and ultimately unloaded. The resident time for the parts in each treating operation or station is determined upon the severity of the soil to be removed from the surface, and also the final thickness and finish appearance required in the finished part. Treatment cycles for rack plating are similar to those required for barrel systems, with appropriate compensation being made for the overall surface to be treated.